Disclosed is a flexible surgical instrument system, comprising a distal structural body comprising at least one distal structural segment each comprising a distal spacing disk, a fixing disk and structural backbones; a proximal structural body comprises at least one proximal structural segment each comprising a proximal spacing disk, a proximal fixing disk and structural backbones; a plurality of cable transmission mechanisms each comprising a gear set and a pulley-cable part, the gear set being operable to transfer a rotational motion to the pulley-cable part; and a driving unit comprising a motion transmission part comprising a plurality of proximal segment turning transmission chains to convert a rotational output into mutually reversed rotational motions, and transfer one of the mutually reversed rotational motions to one of the gear sets.